This application claims the benefit of Korean Patent Application No. 1999-13095, filed on Apr. 14, 1999, under 35 U.S.C. xc2xa7119, the entirety of which is hereby incorporated by reference.
1. Field of the Invention
The present invention relates to a liquid crystal display (LCD) device, and more particularly, to a structure of a liquid crystal display module having a light waveguide plate and a main supporting frame.
2. Description of Related Art
Liquid crystal displays (LCDS) are gaining in popularity for use in systems such as television receivers, computer monitors, avionics displays, aerospace displays, and other military-related displays where the elimination of cathode ray tube (CRT) technology is desirable for several reasons. In particular, CRTs are characterized by large depth dimensions, undesirably high weight, and fragility. Additionally, CRTs require a relatively high voltage power supply in order to sufficiently accelerate electron beams for displaying images.
The aforementioned shortcomings of CRTs are overcome by flat panel liquid crystal displays in which matrix arrays of liquid crystal picture elements or pixels are arranged in a plurality of rows and columns. Patterns of information are thereby defined by the two dimensional array of pixels, which because of differences in the orientation of the liquid crystal material within each pixel, are caused to appear either darkened or transparent.
FIG. 1 is a perspective view illustrating a conventional LCD module, and FIG. 2 is a cross-sectional view taken along line IIxe2x80x94II of FIG. 1. As shown in FIGS. 1 and 2, the LCD module 10 generally includes a display panel 20 comprising two substrates with a liquid crystal layer interposed therebetween, a back light device 30 having a lamp 36 as a light source arranged along a side of the LCD module 10, a metal frame 70 supporting the display panel 20 and the backlight device 30 together with a main frame 40.
The backlight device 30 further includes a protecting sheet 31, a diffusing sheet 32, a prism sheet 33, a light waveguide plate 34, and a reflecting sheet 35, which are stacked in above-described order. The light waveguide plate 34 serves to uniformly direct a light from the lamp 36 to the display panel 20, and its three side walls contact with corresponding portions of the main frame 40. The other side wall 50 of the light waveguide plate 34 contacts with the lamp 36 through a lamp housing 60 that surrounds the lamp 36 (see FIG. 3).
FIG. 3 is a perspective view illustrating a structure of a conventional LCD module having the light waveguide plate and the main frame. As shown in FIG. 3, the main frame 40 has a recessed portion 42 and the light waveguide plate 34 has a protruding portion 34a around a center of its side wall which is perpendicular to the longitudinal direction of the lamp 36. So the light waveguide plate 34 is accommodated in the main frame 40 when the protruding portion 34a is aligned with the recessed portion 42. Movement of the light waveguide plate 34 that may damage the lamp 36 is prevented owing to the engagement of the protruding portion 34a and the recessed portion 42.
FIG. 4 shows a different structure of another conventional LCD module having the waveguide plate and the main frame. As shown in FIG. 4, the main frame 40 has fixing portions 44 at both end portions thereof adjacent to the lamp 36 and the light waveguide plate 34 has recessed portions 34b at locations corresponding to the fixing portions 44 of the main frame 40 such the light waveguide plate 34 is accommodated in the main frame 40. Thus, movement of the light waveguide plate 34 that may damage the lamp 36 is prevented.
However, the structures of the light waveguide plate and the main frame described above have the following disadvantages.
As shown in FIG. 2, since the light waveguide plate 34 is generally fabricated through an injection molding process using a metal mold and the open portion of the mold corresponds to an upper edge of the light waveguide plate 34, it has burrs 38 formed on its upper edge. The burrs 38 are formed after the molding process due to the open portion. When the light waveguide plate 34 having the burrs is accommodated in the main frame 40 or when the light waveguide plate 34 moves, friction between the burrs 38 of the light waveguide plate 34 and the main frame 40 produces alien substances, leading to a bad display characteristics of the LCD.
Next, in general, dimensions of the light waveguide plate vary with the surroundings. And the dimension variation of the light waveguide plate is a product of a length and the coefficient of linear expansion. Therefore, when the coefficient of linear expansion is constant, its dimension variation becomes greater as it get far from a reference point of the light waveguide plate. But the main frame 40 seldom changes its dimension since it is usually made of polycarbonate whereas the light waveguide plate is usually made of acrylic resin. Referring to FIG. 3, note that the side wall 50 of the light waveguide plate 34 is a reference point since at that point the light waveguide plate 34 and the main frame 40 are fixed by the lamp housing 60. Since the protruding portion 34a of the light waveguide plate 34 is far from the side wall 50 of the light waveguide plate 34, the dimension variation difference between the recessed portion 42 of the main frame 40 and the protruding portion 34a of the light waveguide plate 34 is much larger. As a result, variation of a space xe2x80x9cAxe2x80x9d between the recessed portion 42 and the protruding portion 34a becomes as large as about xc2x10.3 mm. Therefore the light waveguide plate 34 may get out of the lamp housing of the lamp 36 during an impact test or being carried, leading to a problem in that light leakage (a bright line) may occur in the vicinity of the end portion of the display panel 20. In order to overcome such a problem, the structures of the light waveguide plate and the main frame in FIG. 4 have been introduced whose the fixing portion 44 and the recessed portion 34b are formed at both end locations adjacent to the lamp 36. In general, between the fixing portion 44 and the recessed portion 34b, a space xe2x80x9cBxe2x80x9d of 0.3 mm is required. This is because the light waveguide plate 34 is expanded during a high temperature test and gets bent so that the sheets 31, 32 and 33 (see FIG. 2) arranged over the light waveguide plate 34 get bent. Thus, space xe2x80x9cBxe2x80x9d of 0.3 mm between the fixing portion 44 and the recessed portion 34b is necessary. However, such a space xe2x80x9cBxe2x80x9d of 0.3 mm causes the light waveguide plate 34 to get out of the lamp housing 60 of the lamp together with dimension variation difference between the light waveguide plate 34 and the main frame 40 due to the surroundings such a temperature and humidity during an impact test or being carried, leading to a problem in that light leakage (a bright line) may occur in the vicinity of the end portion of the display panel 20.
In order to overcome problems described above, a preferred embodiment of the present invention provides a liquid crystal display device having good display characteristics and capable of preventing a bright line from occurring.
In order to achieve the above object, the present invention provides A liquid crystal display device module which includes a backlight device having a) a lamp; b) a lamp housing surrounding the lamp; c) a reflecting sheet for reflecting light from the lamp; d) a light waveguide plate having four side walls, one of the four side walls fixed to the lamp housing and another side wall adjacent to the fixed side wall having a protruding portion, the light waveguide plate being located on the reflecting sheet, and e) a plurality of sheets located on the light waveguide plate; a liquid crystal panel located on the backlight device; a first frame located on the liquid crystal panel; and a second frame assembled with the first frame interposing the liquid crystal panel and the back light, the second frame having a recessed portion formed at a location corresponding to the protruding portion of the light waveguide plate, wherein a distance from the fixed side wall of the light waveguide plate to the protruding portion is sufficiently short so that dimension variation between the protruding portion of the light waveguide plate and the recessed portion of the second frame is small enough to be ignored.
The distance from the fixed side wall of the light waveguide plate to the protruding portion of the light waveguide plate is less than 30 mm. Each upper edge of the four side walls of the light waveguide plate has burrs, and the second frame further includes at least one side wall having an inclined portion formed at a location corresponding to the burrs of the light waveguide plate, the inclined portion having an inclined length and an angle enough not to contact with the burrs. The angle of the inclined portion is about 45xc2x0. The inclined length of the inclined portion is about 0.3 mm.